We request support for a two-day symposium entitled "Endocrinology of Arctic Birds and Mammals" to be held during the annual meeting of the American Society of Zoologists in Los Angeles, 27-30 December 1993. This symposium will focus on field behavior and physiology in arctic breeding populations of birds and mammals. Compared to most temperate latitudes, the arctic environment offers a shorter breeding season, severer conditions at its beginning, sustained inclemency, early winters, and extreme photoperiods. Consequently, arctic breeding populations may have evolved a relative inflexibility of timing of reproduction, a commitment to single breeding efforts and associated insensitivity to stress, and strategies to cope with conflicts between allocating time and energy to reproductive efforts and growth, molting, and fattening in preparation for migration or overwintering. In a highly comparative manner these adaptations are being newly investigated on the level of endocrine mechanisms. This symposium will bring together arctic researchers from six countries to integrate results and investigate common themes and to showcase to the American Society of Zoologists future opportunities for research in the arctic. Themes planned for the symposium are (l) hormonal and neuroendocrine control over pre-migratory fattening, migration, and growth; (2) photoperiodism and melatonin in the arctic; (3) reproductive endocrinology of arctic breeders; (4) endocrine modulation of stress during arctic breeding; and (5) endocrine interrelationships between hibernation and reproduction.